In general, semiconductor materials may be processed in semiconductor technology on or in a substrate (also referred to as a wafer or a carrier), e.g. to fabricate integrated circuits (also referred to as chips). During processing of the semiconductor material, certain processes may be applied, such as forming one or more layers over the substrate, structuring the one or more layers, or contacting the chips. In general, a porous copper layer offers beneficial mechanical properties, for example, in the field of a thick power metallization.
In contrast to a dense layer (bulk copper) a porous copper layer may apply less mechanical and/or thermal stress to the silicon and, therefore, offer the possibility to prepare a thick copper layer on wafer and a chip, without inducing bowing of the wafer or the chip, delaminating from the wafer or the chip, and/or inducing cracks into the wafer or the chip.
Conventionally, the properties of a porous copper layer are adjusted by changing the preparation parameters, e.g. the source material (particle size or additives) or the processing parameters (deposition parameter, furnace parameter, annealing parameter). This adjustment is strongly limited to the range of the preparation parameters and, therefore, is rather narrow. Further, this adjustment fails in sealing the pores, requires additional effort, and is highly sensitive to the used copper particle containing paste, which reduces the scope of adapting the adjustment to other paste compositions.
Alternatively, two layers may be formed by printing different copper particle containing pastes or a metal-precursor paste over each other. This process may only be able to adjust the spatial porosity of the porous copper layer, fails in sealing the pores, requires additional effort, and is sensitive to the combination of the used copper particle containing paste.
Alternatively, the porous copper layer may be coated by electrochemical deposition or electro-less-chemical of a metal. This may result in the inclusion of the used electrolytes, increasing a risk of impurities and contamination or other consequences as a reduced reliability or damage to the device.